In U.S. Pat. No. 3,814,483, issued June 4, 1974 to Ronald W. Coiner et al and assigned to the assignee of the present application, there is shown and described a blending valve device for a combined fluid pressure and dynamic vehicle brake apparatus wherein a brake-applying fluid pressure is established by a self-lapping valve device that is operable by a spring-biased lever, having a fulcrum adjustable according to the load on the vehicle, in response to a reduction in a dynamic braking effort, to provide a corresponding fluid pressure retarding force whereby the combined reducing dynamic braking effort and this fluid pressure retarding force provides a vehicle retarding force that is in accordance with the selected degree of operation of an operator-controlled brake control means. The brake apparatus disclosed in the above-mentioned United States Patent embodies means for enabling effecting only a limited emergency brake application.
Accordingly, it is the general purpose of this invention to provide a novel brake apparatus for an electrically-propelled vehicle having dynamic brakes wherein a spring disposed on one side of a brake-applying piston is effective, as the dynamic braking effort decreases, to transmit via the piston a service brake-applying force that is proportional to an operator-controlled reduction in the pressure of fluid in a chamber on the other side of the piston. An emergency brake-applying force is provided cojointly by this spring and the fluid-pressure-force resulting from an operator-controlled supply of fluid under pressure to the one side of the piston.